(1) Field of the Invention
The present invention relates to a international roaming-capable mobile communication terminal that has a response message transmission function.
(2) Description of the Related Art
Conventionally, telephones have a function for playing an audio response message such as “I'm unable to come to the phone right now . . . ” when the user of the telephone is unable to answer the telephone for reasons such as being absent from home (see Reference 1).
This function is included not only in land-line telephones, but also in mobile communication terminals, such as mobile telephones, with which audio communication is possible.
Since mobile telephone are portable, there have been demands from users to be able to use the mobile telephone that the user uses in his or her own country, and the functions of the mobile telephone that can be used in the user's own country, when the user goes overseas.
In response to such demands, international roaming services have been implemented that enable users to use the mobile telephones that they use in their own country overseas.
However, an international roaming-capable mobile telephone must support the audio compression method used in the regions in which the mobile telephone is to be used. This is because, presently, several different types of audio compression are used internationally.
Since one audio compression method, such as EVRC, is used in Japan, response message data compressed in this format is not able to be listened to in another country that uses another audio compression method such as QCELP. Tin other words, in order to listen to audio encoded according to a particular audio compression method, it is necessary to decode an encoded digital signal in that format, and convert the decoded signal to an analog signal. Consequently, when a different audio compression method is used, the encoded digital signal is unable to be decoded correctly, and the audio cannot be listened to. This can be seen in Japanese Laid-Open Patent No. H06-78049.